1. Field of the Invention
The present invention relates to solenoid actuators for valves and the like in general and in particular to an actuator for valves for control of fluid flow. More particularly still, it relates to a fail-safe actuator suitable for controlling flow of toxic substances or the like hazardous or corrosive fluids.
2. Prior Art
U.S. Pat. No. 4,259,653 granted Mar. 31, 1981 to McGonigal titled "Electromagnetic Reciprocating Linear Actuator with Permanent Magnet Armature" closes a spring-less linear actuator, especially useful as a print wire drive. A permanent magnet armature is driven from a rest position on a pole piece by magnetic repulsion upon energization of a solenoid by a D.C. pulse. The armature is fixed to a print wire which rebounds from a printing medium, thereby returning the permanent magnet toward the rest position, where it is held, without bouncing, by the magnetic attraction between the armature and the pole piece of the solenoid, which is now de-energized.
U.S. Pat. No. 5,546,063 granted Aug. 13, 1996 to Hoffman titled "Magnetic Field Solenoid" discloses an electrical coil having a central opening in which is fixedly located a rod formed of a material of the type capable of being magnetized when in a magnetic field. A plunger is supported for movement toward and away from one end of the rod. A permanent magnet is supported by the plunger. In one embodiment the permanent magnet is located such that the plunger and permanent magnet are held next to the coil when the coil is in a deactivated condition. When the coil is activated, the magnetic field produced by the coil repels the permanent magnet and hence the plunger away from the coil. The polarity of the permanent magnet can be reversed in position such that normally the permanent magnet and hence the plunger are normally repelled away from the rod end when the coil is in a deactivated condition. When the coil is activated in a given manner, the magnetic filed of the coil pulls the magnet and hence the plunger next to the coil. In another embodiment two permanent magnets are attached to opposite ends of a plunger of the type unaffected by a magnetic field to form a push-pull type of solenoid.
U.S. Pat. No. 5,497,135 granted Mar. 5, 1996 to Wisskirchen et al. titled "Bistable Electromagnet, particularly an Electromagnetic Valve" discloses a bistable electromagnet moved from one operating position into the other by a short direct current pulse, the next pulse following in each case having the opposite current direction. The essential factor in this is a permanent magnet which is arranged in the core area and which holds the armature against the action of an armature spring in one operating position. An electromagnet constructed in this manner can be produced without tolerance calibration and requires less control power when the permanent magnet is carried freely movably between two end positions in the direction of armature movement in a hollow space of the coil core. The coil core can be constructed as a pot, at the bottom of which the permanent magnet is magnetically held whilst the permanent magnet is held in the other end position by a stop in such a manner that its side facing the armature is approximately flush with the edge of the pot.
The closest prior art known is U.S. Pat. No. 4,534,537 granted Aug. 13, 1985 to Zukausky titled "Pilot Operated Valve Assembly" discloses a pilot operated valve assembly including a flexible diaphragm which selectively engages a valve seat to open and close a fluid passage through the valve. The diaphragm has a plurality of filtering apertures and an inward peripheral attaching projection. A diaphragm insert is frictionally received in the diaphragm. The diaphragm insert has a pilot supply aperture in fluid communication with a peripheral recess extending inward from a peripheral edge. The diaphragm filtering apertures are disposed in fluid communication with the peripheral recess and the pilot supply aperture. The insert peripheral edge has a peripheral valley for receiving the peripheral projection of the diaphragm. The insert has a pilot outlet aperture which is selectively opened and closed by an armature assembly. A guide shell aligns the armature assembly with the pilot outlet aperture and defines a pilot reservoir with the diaphragm. This United States patent is incorporated herein by reference.